1. Field of the Invention
The present invention relates to a throttle control apparatus which controls, in accordance with the depression of an accelerator pedal, a motor so as to open and close a throttle valve by means of a controller, thereby controlling the amount of inlet air fed to an internal combustion engine.
2. Description of Related Art
A throttle control apparatus has been developed recently in which an electronic throttle control is carried out. For instance, a motor is actuated by a controller in accordance with depression of an accelerator pedal, and a throttle valve is opened and closed accordingly.
Japanese Unexamined Patent Publication (KOKAI) No. 4-231,627 discloses one such throttle control apparatus. In this throttle control apparatus, a motor is actuated in accordance with the depression of an accelerator pedal and a throttle valve is electrically controlled during ordinary driving. On the other hand, when the motor is turned off due to a failure in the electric system, an electromagnetic clutch is actuated to mechanically engage the accelerator lever and the throttle lever, thereby opening the throttle valve in accordance with the depression of the accelerator pedal. Thus, with this throttle control apparatus, it is possible to drive the vehicle to a repair shop even when the motor is turned off as a result of a failure in the electric system or the like.
However, the throttle control apparatus disclosed in the aforementioned publication requires the electromagnetic clutch, The electromagnetic clutch must be connected to an electric power source so as to apply a predetermined voltage thereto even during ordinary driving. This is problematic in that it requires a large electric power consumption.
Japanese Unexamined Patent Publication (KOKAI) No. 59-122,742 discloses another throttle control apparatus. As illustrated in FIG. 8, in this throttle control apparatus, a motor 502 is actuated in accordance with signals output by an accelerator sensor 501 which detects the depression of an accelerator pedal 500, a motor pulley 503 is rotated in the direction of the arrow P1 of the drawing, and consequently a throttle valve 506 is electrically controlled by way of a cable 504 during ordinary driving. On the other hand, when the motor 502 is turned off due to a failure in the electric system, an accelerator pulley 507 is rotated by way of a cable 508, in accordance with the depression of the accelerator pedal 500, in the direction of the arrow P1 of the drawing so as to mechanically engage its protrusion plate 507a with a protrusion plate 503a of the motor pulley 503. The motor pulley 503 is rotated in the same direction (i.e., in the direction of the arrow P1), and consequently the throttle valve 506 is opened by way of the cable 504. In this throttle control apparatus, the protrusion plate 503a and the protrusion plate 507a are off-set or separated from each other in the circumferential direction. The off-set distance between them inhibits the protrusion plates 503a and 507a from engaging each other.
However, when controlling a driving vehicle, situations arise where the throttle valve 506 should be controlled so as to operate in the valve-closing direction regardless of the depression of the accelerator pedal 500. This type of control is generally called traction control (hereinafter simply referred to as "TRC" control), and, for instance, is intended to prevent vehicles from slipping during starting or driving on iced roads. When such TRC control is carried out, although the accelerator pulley 507 is rotated in the direction of the arrow P1 because of the depression of the accelerator pedal 507, the motor pulley 503 is rotated by the motor 502 in the direction of the arrow P2. As a result, the protrusion plate 503a mechanically engages the protrusion 507a, and accordingly there arises difficulty with respect to controlling the throttle valve 506 in the valve-closing direction. In addition, the mechanical engagement between the protrusion plates 503a and 507a causes shock in the accelerator pedal 500. In order to overcome these problems, it is necessary to increase the off-set distance between the protrusion plates 503a and 507a, but this inevitably leads to a larger throttle control apparatus. Further, even if the off-set distance between the protrusion plates 503a and 507a can be increased in the circumferential direction in order to prevent the protrusion plates 503a and 507a from mechanically engaging each other, the protrusion plate 507a must be rotated by the increased off-set distance in the direction of the arrow P1 when the motor 502 is turned off. Consequently, there arises another problem in that, when the motor 502 is turned off, the degree of opening of the throttle valve 506 is restricted and can hardly be increased.
As can be appreciated from the foregoing description, in the throttle control apparatus disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 59-122,742 and illustrated in FIG. 8, the protrusion plate 503a and the protrusion plate 507a are separated from each other in the circumferential direction to a certain extent, and are disposed to face each other when electronic throttle control is carried out by utilizing the motor 502. However, they cannot be shunted to their siding positions when electronic throttle control is carried out by utilizing the motor 502.